It was not so much that Nico Rosberg's dominant victory in Singapore was his eighth win of the season - Hamilton has won six times - or that the German now holds the championship lead for the first time since after the British Grand Prix in early July.

It was more what happened on Saturday, when Rosberg took pole position with what was probably the lap of his career.

In fact, over his whole career, Hamilton has only ever been out-qualified by a team-mate by a margin that big on six previous occasions in 182 grands prix - once by Fernando Alonso in 2007, once by Heikki Kovalainen in 2008, and four times by Jenson Button.

Why was Hamilton so slow?

Hamilton had little time to get accustomed to his car in Singapore

So what went wrong for Hamilton in Singapore, on a track where he has often excelled in the past?

In this case, it seems a simple matter of a bad weekend, in which a combination of circumstances combined to leave him adrift.

It started with Hamilton and Rosberg choosing divergent set-ups in the first practice session on Friday. Hamilton emerged as the faster Mercedes driver but was struggling with locking brakes, a problem that continued into the next session that evening.

Halfway through the second session things started to go badly wrong. Three times Hamilton tried to set a lap time on his qualifying simulation on the ultra-soft tyres and each time he made a mistake.

Then his car developed a hydraulic leak and he missed the second half of the session, when the drivers do their core race preparation work.

In Saturday's final practice, Hamilton did only nine laps, again suffering with locking brakes, again failing to get in a time on his qualifying simulation laps.

After Hamilton qualified third behind Rosberg and Red Bull's Daniel Ricciardo, Mercedes F1 boss Toto Wolff said Hamilton's car was "not where it should have been after free practice one".

He added: "It's not easy to find the right compromise between the set-up of the car and getting the tyres in the right window and giving the driver a confident feeling. Here we failed.

"He didn't have a car today that was able to extract all the performance. The set-up was not right."

Wolff blamed this on the lack of running time in practice.

The world champion has only been beaten in qualifying by the margin he was this weekend six times in 182 races

"Lewis was lacking possibility to run the car so he could not find out what was the right direction for him to go," he said. "You cannot just guess.

"The approach he chose was probably right. He stayed where he was without deciding on a particular avenue because he didn't know. Then it was just down to the lack of running.

"You have to give the driver running time and if you can't run the car here, you can't find what set-up works for you.

"And you can't really gain confidence in the car either. This was less of his particular problem, it was more that the car did not generate the amount of grip that Nico had."

A wrong set-up leads to all sorts of problems. For a start, the car is fundamentally not as fast. For another, the driver lacks confidence in its behaviour, feels he can not rely on what it is going to do, and by extension cannot push to the limit.

On a track like Singapore with 23 corners, bumps and unforgiving concrete walls everywhere, this has a bigger effect than almost anywhere else.

"If you are lacking laps in free practice in Singapore and lacking direction where to take the set-up, it is a vicious circle," Wolff said. "Confidence is key around Singapore.

"Then if your team-mate gets out of the blocks in the way Nico did this weekend, it becomes very difficult. Lewis is the first to acknowledge that."

Hamilton has won twice at Singapore's Marina Bay

One question still hangs in the air, though. In the past, if Hamilton has been struggling for set-up, he has sometimes adopted Rosberg's as a way of getting back on track. But that did not happen in Singapore.

As Hamilton put it after the race: "It doesn't always go the way you want it go and this has definitely been a difficult weekend for me and my side of the garage. But we will reunite and regather, understand where we went wrong and try to rectify it for the next race."

Rosberg better than ever

This was not just about Hamilton's problems, though. Singapore also saw Rosberg on a level he has perhaps never reached before. Certainly that is what Wolff believes.

"I have known him since 2013 and that is the best Nico Rosberg I have ever seen throughout the weekend," added Wolff.

"We have the tendency of saying Lewis has an awesome pace and this is what we have seen with Nico this weekend. He was just blindingly fast."

Rosberg rated his qualifying lap as one of the "top three" of his career. One suspects the sample was rather smaller than that.

Rosberg's record in Singapore had been poor before this race

In fact, when he was pressed on that claim and asked to name the other two, he said: "Monaco 2013, for example. I can't think of the other."

In Monaco three years ago, Rosberg beat Hamilton to pole by 0.091secs. So it is pretty safe to say this was indeed the lap of his career.

"It is the feeling of how it comes together, that I feel one with my car, that I can go beyond the limit without making a mistake," Rosberg said. "It is a special feeling."

In the race, too, he was flawless. Some will doubtless carp and say it was yet another race Rosberg won from the front, that he is less effective when he has to fight back. And they may have a point.

But this was a champion's drive and it has put him back in control of the season.

Can Hamilton come back?

"Nico just did an exceptional job this weekend and we didn't," explained Hamilton. "What's it going to take [to get the lead back]? Just some good weekends, which we've had in the past."

Hamilton has lost no opportunity to remind people this year that he is fighting a rearguard battle, after the technical problems that put him on the back foot early in the season and which were largely responsible for Rosberg building a 43-point lead after four races.

When Hamilton turned that into a 19-point advantage in his favour with six wins from the next seven races, it looked like it was game over and title number four was as good as in the bag.

But the knock-on effect of those early season problems led to engine penalties in Belgium last month, handing Rosberg victory on a plate. Since then, Hamilton has had a bad start in Monza, which turned a potential win into a second place, and now a bad weekend in Singapore.

Afterwards he was downcast but defiant.

"All in all, with everything that's gone on this year, I'm still in the fight," he said. "There's still a long way to go and I'm going to give it everything I've got.

On the evidence of Singapore, this is going to be his toughest challenge yet.

A word for Ricciardo

There were some good battles down the field but this race was, frankly, pretty tedious at the front for much of its duration.

Until, that is, Mercedes decided to switch Hamilton to a three-stop strategy in order to beat Kimi Raikkonen's Ferrari to third place. That led to a chain reaction, with first Raikkonen and then Ricciardo following suit.

Mercedes could not react with Rosberg because he was delayed by traffic at the crucial time and would have lost the lead had he stopped, so he had to stay out and hope he had enough left in his tyres to hold off the flying Red Bull.

It led to a gripping climax, in which Ricciardo crossed the line 0.4secs behind Rosberg, after closing a 25-second margin in 14 laps.

Daniel Ricciardo has out-qualified team-mate Max Verstappen 9-2 this season

It was a brilliant drive by the Australian to top a superb weekend.

He and Red Bull knew that Singapore would give them their best chance of the remaining races to beat Mercedes to a fair-and-square victory - something they would have done in Monaco had a pit-stop error not delayed Ricciardo.

In fact, by rights, Ricciardo should have had two wins this year - he only lost in Spain because of a questionable strategy call when he was leading, which resulted in team-mate Max Verstappen winning instead.

There is even a strong case to be made for Ricciardo being the driver of the season so far.

He has had one or two slightly shaky weekends, but, by and large, has been terrific all year. And despite the hype around Verstappen, Ricciardo is beating the Dutchman - a great talent for the future though he undoubtedly is - pretty comprehensively.

It is now 9-2 to Ricciardo in qualifying since they became team-mates and he has outscored Verstappen by 23 points, notwithstanding the team shooting him in the foot in Spain and Monaco.

Ricciardo accepts it will now take something unusual to make that win happen.

"With some rain, yeah," Ricciardo said. "I think in dry circumstances this was our best shot.

"We got within half a second but after the race I said on the radio to the team that we will win this year. We'll get a downpour somewhere, that'll hopefully throw a few curved balls and we can get the victory we're after."